Large Networks Present Visualization Challenges
Bill Hibbard
Space Science and Engineering Center
University of Wisconsin - Madison
November 99 Columns
Visfiles
I seem to have lots of visualization connections with Australia, which is nice, because it means that I sometimes get to travel to Oz. I’ve asked Drew Whitehouse to contribute this VisFiles column describing the fascinating visualization work at the Australian National University.
— Bill Hibbard
Building Screen Based Immersive Virtual Environments on a Budget - the Wedge
Drew Whitehouse
Supercomputer Facility
Australian National University
Introduction
In early 1997, Professor Rod Boswell and Dr. Henry Gardner of the Australian National University (ANU) Plasma Research Laboratory returned to Australia from a trip to the U.S.A. where they had experienced the CAVE [4] at the Argonne National Laboratory. They had the notion that a two wall CAVE-like device would be an interesting and useful project if it could be achieved without using expensive high-end workstations. They approached the ANU Supercomputer Facility (ANUSF) visualization programmers and challenged us to work with them to build such a device. Two years later we have built three, including one installed at the Powerhouse Museum, a high profile technology museum in Sydney, Australia [6]. We have named our system the "Wedge."
I would like to describe some of our experiences in building the system, and the applications which have been developed to date.
Why
The initial goal of the project was to build a system that would be an engaging platform for teaching undergraduate and graduate students scientific visualization techniques as part of an educational program in computational science. Because student numbers in traditional sciences like mathematics and physics have been waning in recent years, Boswell and Gardner felt that there was a need to move towards new and innovative teaching environments. As a supercomputer facility it wasn’t out of the question to purchase a commercial system, but we felt that for pedagogical reasons we could gain more by building a system from the ground up, using low cost components, with the physics group building the hardware and ANUSF visualization programmers developing the software. It also reduced the burden on the developers to justify the costs of a high-end setup by running the facility as a partially commercial venture, which seems to be a common model in the screen based virtual environment community. We wanted to make the cost affordable to medium-sized enterprises and research groups.
How
Our first challenge was to find a workstation that could produce dual screen synchronized stereo 3D graphics at a reasonable speed, ideally programmed via a standard OpenGL API. Although many manufacturers are now selling fast OpenGL graphics cards for PCs, very few are adding stereo capabilities, and even fewer can provide multi-channel output. After talking to quite a few manufacturers, and considering the possibility of using multiple linked low-end workstations (e.g. SGI O2s), we settled on an Intergraph VX25 graphics system and subsequently confirmed that it was ideal for our experiment.
Figure 1: The (portable) first Wedge prototype.
Figure 2: The latest Wedge built at the ANU.
The first screen system built had 1.5 meter square walls and was designed to be relatively portable (see Figure 1). The center of the screens are welded plastic and provide a very concise corner. The screens were fixed to an aluminum frame using rubber bands that gave the system a trampoline like appearance. We have since moved to a neater press stud arrangement. The museum installation has 2.9m x 2.3m screens that rise from the ground, and the new system at the ANU has 4m x 2.2m screens for a very large field of view (see Figure 2).
For our initial experiments we developed a small C++ class library that abstracted away the handling of drawing on multiple walls and projection math allowing users to provide their own OpenGL drawing routines. However one of our main goals with the project has been to develop a system under which non-expert graphics programmers can quickly develop applications. For this we have built our current "pSpace" system which is a python scripted wrapping of the SGI Cosmo3D scene graph API with extra functionality that manages low-level threads for event management, communication with tracking devices and drawing on multiple stereo channels. A simple application can be built with as little as 20 lines of code. The python scripting language [7] has proven to be exceptionally flexible for building scientific visualization applications. We use the python "Numeric" array and "NetCDF" extension modules to read and transform scientific data into graphic representations. The ability to extend python with small dynamically loaded modules allows us to bring new functionality into the system without building a monolithic single application. When python performance becomes too expensive the bottleneck code is rewritten in C++ and dynamically loaded. The pSpace system works under Windows 9x/NT and SGI Irix, so we can easily move between PCs and our Onyx2 Infinite Reality system depending on performance requirements. It also allows students to develop applications on affordable personal machines.
Example Applications
The following are a sample of the applications that have been developed under the pSpace system and demonstrated on the Wedge over the last six months.
Powerhouse Museum Exhibit
The ANU was approached by the curators of Sydney’s Powerhouse Museum in late 1998 to develop an exhibit for their Universal Machine permanent exhibition. The exhibition "looks at the computer and seeks to understand what it is, what it can do, why it was developed, and how it works." One of the themes they explore is simulation and visualization and it was felt that a Wedge was suitable for illustrating these concepts in a powerful and engaging way.
We developed a six-minute program showcasing ANUSF scientific visualization work. The program begins with an introduction to stereo imaging explaining how the viewer is presented separate left and right images via the stereo glasses. This is followed by a visualization of the vibrational modes of a buckminsterfullerene molecule (a bucky ball) and models from the minimal surface work described below. We then present some interesting models of knots and linkages, and finally we show a model of the Heliac plasma device installed at the National Plasma Fusion Research Facility at ANU (our collaborators in the Wedge project) [3].
Figure 3: School children in the Powerhouse Museum’s Wedge.
Figure 4: Triply periodic, minimal, hyperbolic surface with an embedded 3D crystal lattice.
Due to the constraints of the museum environment we used a joystick for navigation and interactivity. This had the beneficial side effect of approximately fixing the viewer’s position in the environment, negating the need for cumbersome and expensive tracking devices. Another benefit, we soon realized, was that most children are already expert joystick operators with (far too?) many hours logged on game consoles. The first thing they do when they grab the handle is push and pull it in every direction, then push every button on the handle. Through this experimentation they master the interface in roughly 10 seconds (see Figure 3). Adults seem to be more reticent. We initially had one of the buttons on the joystick reset the viewer’s position, thinking that this would stop people from becoming lost for any length of time. However it was not unusual to have an adult holding the button down for the entire length of the program, wondering why nothing was happening. The reset button is now a separate button beside the joystick. So the lesson learned was that we had to simplify the interface for adults!
With the short development time allowed for this project, we didn’t achieve as much interactivity as we had desired. We’re currently working with other organizations on similar projects and hope to be able to develop engaging exhibits that utilize the Wedge’s ability to interact with, as well as navigate around, three dimensional objects and spaces. Regardless of this shortcoming the exhibit has been a great success. It is many people’s first experience in an immersive environment and as such seems to be a positive one. The author had much pleasure answering the question of one excited young participant - "how did you get a cool job doing work like this?" by replying "I did a university degree in math." I like to think that they went away with plans to try a bit harder at their next math class. The museum has approximately 600,000 visitors per year, primarily school groups.
Minimal Surfaces
Professor Stephen Hyde and Stuart Ramsden have been using pSpace in the Wedge to investigate the link between crystallographic 3D lattices and graphs in 2D hyperbolic space. By embedding 2D networks within Periodic Minimal Surfaces, 3D lattices can be generated which correspond to chemical systems [2]. The analysis of these complicated 3D structures is greatly enhanced by the immersive stereo display of the Wedge (see Figure 4).
Education
The pSpace system is being used by computer science and engineering undergraduates in a diverse range of visualization projects including architectural walkthroughs, engineering visualization, information visualization and distributed virtual environments.
Approximately 1,500 people have been shown through the ANU wedge over the last 12 months including K-12 school groups, politicians and various industry representatives.
Art History
The ANUSF Vizlab has been collaborating with Professor Michael Greenhalgh of the ANU’s Art History Department to build a comprehensive image and VRML database of the Javanese Buddhist stupa Borobudur using a vast photographic archival record made by the Dutch who renovated the structure during the 1920s [1]. The initial project was completed for CD-ROM and WWW delivery, but a VRML 2.0 viewer has since been developed under pSpace by Ajay Limaye, allowing us to tour this magnificent monument in the Wedge environment. We hope this application can be polished for presentation in a museum exhibition at a future date.
Future
We are currently adding a spatial audio system to the pSpace software, which we hope will enhance the immersive experience and allow us to experiment with data sonification. We are also interested in integrating the software into the Plasma Research Group’s Heliac diagnostics system. We will continue to develop the system for use as a teaching platform in a diverse range of fields, both in the sciences and the humanities. We plan to investigate the feasibility of building a Java3D interface to the Wedge screen setup, spurred to action by the column editor’s recent VisFiles column [5].
Acknowledgments
I would like to thank Rod Boswell and Henry Gardner who provided the initial motivation and who have continued to work for and support the Wedge project. Peter Alexander of the ANU Plasma Research Laboratory built the various generations of Wedge hardware. I would also like to acknowledge my fellow visualization programmers at the ANUSF Vizlab, Stuart Ramsden and Ajay Limaye, who continue to create applications that drive the development of the pSpace software. John Hirsch provided photographs of the Wedge in use at the Powerhouse Museum.
References
- Australian National University Borobudur Project, http://vandyck.anu.edu.au/borobudur/.
- Australian National University Mesoscale Project, http://mesoscale.anu.edu.au/.
- Australian National University Plasma Research Laboratory, http://rsphysse.anu.edu.au/prl/.
- Cruz-Neira, C., D. J. Sandin, T. A. DeFanti, R. Kenyon and J. C. Hart. The CAVE, Audio Visual Experience Automatic Virtual Environment, Communications of the ACM, June 1992.
- Hibbard, Bill. "Top Ten Visualization Problems," VisFiles column, ACM SIGGRAPH Computer Graphics, 33(2) May 1999, http://www.siggraph.org/publications/newsletter/v33n2/columns/hibbard.html.
- The Powerhouse Museum Universal Machine exhibition, http://www.phm.gov.au/universal/.
- The Python programming language, http://www.python.org/.
Drew Whitehouse has been working in scientific visualization at the ANU Supercomputer Facility since 1990. Over that time he has worked on a broad spectrum of visualization projects, concentrating on virtual environments for the last few years. He has also worked commercially developing computer graphics software and as a freelance animator. He has a degree in mathematics from the University of Queensland. Bill Hibbard's research interests are interaction techniques, data models and distributed architectures for numerical visualization. He leads the SSEC Visualization Project and is primary author of the Vis5D and VisAD systems. He has degrees in mathematics and computer science from the University of Wisconsin - Madison.
Drew Whitehouse
Supercomputer Facility
Australian National University
0200, ACT
Australia
Tel: +61-0-2-6249-5985
Website
Bill Hibbard
Space Science and Engineering Center
1225 W. Dayton Street
Madison, WI 53706
Tel: +1-608-253-4427
Fax: +1-608-263-6738
Website
The copyright of articles and images printed remains with the author unless otherwise indicated.